Friday, 12 June 2009

Imagine one of your hands having a life of its own, reaching, grabbing and clutching whatever it likes. Such a condition exists, is known as anarchic hand syndrome, and usually develops after brain damage to the front of the brain. One famous sufferer is Dr Strangelove in the eponymous Stanley Kubrick film. Now Al Cheyne and colleagues think they've found a way to simulate this bizarre condition in the lab.

Cheyne's team had 16 participants perform a test of sustained attention. Whenever a number between "1" and "9" appeared on the computer screen, participants had to press the "M" key on the keyboard with their right hand, with one exception. On the rare occasions that the digit "3" appeared, they had to suppress their usual response and instead press the "Z" key with their left hand.

Whenever they made an error on one of these rare switch trials, the participants were asked to say how much they felt in control of the action, and how much they felt their hand was in control.

Errors on switch trials occurred on average about 35 per cent of the time, and led to the odd sensation of knowing that one should be pressing the "Z" key with the left hand, but instead seeing one's right hand go on ahead and press the "M" key.

Crucially, the participants' reports showed that these errors were associated with the sense that their hand was in control more than they were - a phenomenon the researchers dubbed "attention-lapse induced alienation".

Everyday we perform apparently automatic actions, from brushing our teeth to driving to work, and yet they don't lead to this feeling of alien control. Cheyne's team said the key factor leading to the sense of lost control (both in the lab, and in anarchic hand syndrome) is that the errant action(s) continues in direct conflict with a different consciously intended goal. "For alienation to occur, the automatic action must, as it were, be caught in flagrante delicto and continue even as we intend otherwise for us to imbue it with an alien source," they said.